ML20147A541
| ML20147A541 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 07/28/1980 |
| From: | Christopher Hunter NRC/RES/DRA/PRB |
| To: | |
| Littlejohn J (301) 415-0428 | |
| References | |
| LER 1980-031-00 | |
| Download: ML20147A541 (5) | |
Text
C Accession Number: 158229 te: July 28, 1980
- Scram Discharge Volume Fails to Drain and Alarms Clear at Dresden 3 failure sequence was:
Data on BWR scram system was being gathered as requested by IE Bul-letin 80-17.
The reactor was manually scramed, and the system was aligned to obtain data.
Approximately 8 minutes after scram the scram instrument volume (SIV) level instrumentation indicated that the scram discharge volumes (SDVs) had drained.
Ultrasonic test, however, showed that the 4-inch piping of the west SDV was still 80% full.
The ball check valve (vacuum breaker) on the west SDV alternate vent path was found to be stuck closed.
The cause for the failure of west side SDV drainage is believed to be due to unavailability of the normal vent path combined with un-availability of the alternate vent path. Both SDVs are normally vented via a common header that is piped to a vented tank, the RBEDT (reactor building equipment drain tank). [At the time of this event the level in the RBEDT was reported to be above normal, such that the SDV vent header was emersed and could not be vented. The east SDV would also have been prevented from draining if its alternate vent path was not functioning (i.e., if its ball check valve was stuck closed).]
rrective action:
. The west ball check valve was manually opened establishing a positive venting path, and the SDV drained.
A daily ultrasonic test to verify SDV drainage and scram volume availability was immediately implemented.
Both east and west ball check valves were removed and cleaned and were shown to operate satisfactorily.
An alternate continuous vent path was established that only depends on the SDV vent valves and not the ball valves.
Installation of a continuous water level monitoring system was to be investigated.
sign purpose of failed system or component:
The scram system is designed to rapidly insert the control rods in event of required shutdown.
Damage been manually opened, SDV still 80% full position, allow-the level switches on due to unavailable ing SDV to drain the scram instrument normal and backup volume cleared, indi- vent paths cating that the SDVs had drained No No - reactor already scrammed No No C 158229 - Actual Occurrence of the Scram Discharge Volume Fails to Drain and Alarms Clear at Dresden 3
Control Adequate System Operates Adequate Core Core Initiated_ Cooling Damage J'yNo 1 Yes 2 No 3 Yes 4 Yes 5 Yes 6 No 7 (F) lN Yes 8 Yes 9 Yes 10 NSIC 158229 - Sequence of Interest for Scram Discharge Fails, to Drain and Alarms Clear at Dresden 3
ACCESSION NUMBER: 158229 NO.: 80-031 OF LER: July 28, 1980 OF EVENT: July 19, 1980 EM INVOLVED: Scram system ONENT INVOLVED: Scram discharge volume E: Mechanical failure of vent check valve and level switch ENCE OF INTEREST: Loss of feedwater AL OCCURRENCE: Failure of scram discharge volume (SDV).to drain and SDV level instrument to transmit correct signal TOR NAME: Dresden 3 ET NUMBER: 50-249 TOR TYPE: BWR GN ELECTRICAL RATING: 794 MWe TOR AGE: 9.5 years OR: General Electric HITECT-ENGINEERS: Sargent & Lundy ATORS: Commonwealth Edison TION: 9 miles east of Morris, Illinois TION: 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (estimated) (service failure duration would have been controlled by emptying of the RBEDT. The duration is based on an assumed RBEDT drainage once per day (24 h).
T OPERATING CONDITION: 0% power (test scram just initiated)
OF FAILURE: Inadequate performance; made inoperable; VERY METHOD: Test required by IE Bulletin 80-17
at NSIC, it appears that overall the west SDV was on the order of 40% full. Even with the CRD seal leakage and bypass flow accumulating nominally in excess of 5 gpm, the SDV may have been able to accommodate at least a partial scram. See also NUREG-0090, Vol. 3, No. 2.